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U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006-5023

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Table 5. Calculated depths of pier scour, contraction scour, and angles of attack at pier 3, and associated variables, Tanana River at Nenana, Alaska.

[Abbreviations: HEC-RAS, Hydrologic Engineering Center River Analysis System; RMA2, Resource Management Associates; ft, foot; ft/s, foot per second; ft/s², foot per square second; ft³/s, cubic foot per second]

Pier Scour calculated using output from one-dimensional HEC-RAS model			Discharge scenario
			Discharge, Aug. 17,1967	100-year flood			500-year flood
				Low flow	High flow		Low flow	High flow
Velocity at nose of pier (ft/s)	v1		10.51	10.81	8.90		12.21	10.23
Depth at nose of pier (ft/s)	y1		21.3	19.6	22.9		21.3	24.5
Gravity constant (ft/s2)	g		32.17	32.17	32.17		32.17	2.2
Froude number at nose of pier	Fr = v1/(gy1)1/2		.40	.43	.33		.47	.36
Pier shape			Sharp nose	Sharp nose	Sharp nose		Sharp nose	Sharp nose
Pier shape correction factor	K1		1.0	1.0	1.0		1.0	1.0
Angle of attack (degree)	AA		15	15	15		15	15
Pier width (ft)	a		14.0	14.0	14.0		14.0	14.0
Pier length (ft)	L		62	62	62		62	62
Ratio	L/a		4	4	4		4	4
Angle of attack correction factor	K2 = f(AA, L/a)		1.6	1.6	1.6		1.6	1.6
Pier Scour (ft)	yps		37.8	37.9	35.6		40.3	38.1

Pier Scour calculated using output from two-dimensional RMA2 model			Discharge scenario
			Discharge, Aug. 17,1967	100-year flood			500-year flood
				Low flow	High flow		Low flow	High flow
Velocity in the X direction at nose of pier (ft/s)	vx		-10.93	-11.13	-8.82		-12.68	-10.20
Velocity in the Y direction at nose of pier (ft/s)	vy		-1.42	-1.72	-0.84		-1.83	-0.98
Resultant velocity at nose of pier (ft/s)	v1		11.02	11.36	8.86		12.81	10.25
Depth at nose of pier (ft/s)	y1		23.9	22.4	26.5		24.1	28.0
Gravity constant (ft/s2)	g		32.17	32.17	32.17		32.17	32.2
Froude number at nose of pier	Fr = v1/(gy1)1/2		.40	.42	.30		.46	.34
Pier shape			Sharp nose	Sharp nose	Sharp nose		Sharp nose	Sharp nose
Pier shape correction factor	K1		1.0	1.0	1.0		1.0	1.0
Angle of flow (degree)			263	261	265		262	265
Angle of pier (degree)			248	248	248		248	248
Angle of attack (degree)	AA		15	13	17		14	17
Pier width (ft)	a		14.0	14.0	14.0		14.0	14.0
Pier length (ft)	L		62	62	62		62	62
Ratio	L/a		4	4	4		4	4
Angle of attack correction factor	K2 = f(AA, L/a)		1.6	1.5	1.6		1.5	1.6
Bed condition (dunes) correction factor	K3		1.1	1.1	1.1		1.1	1.1
Pier Scour (ft)	yps		38.9	38.0	37.3		40.8	40.0

Live-bed contraction scour simulated using output from one-dimensional HEC-RAS model			Discharge scenario
			Discharge, Aug. 17,1967	100-year flood			500-year flood
				Low flow	High flow		Low flow	High flow
Total discharge in Tanana River main channel (ft3/s)	Q		158,000	150,000	149,000		187,000	185,000
Exponent determined from mode of bed material transport	K1		.69	.69	.69		.69	.69
Discharge in main channel of approach section (ft3/s)	Q1		156,700	148,000	142,000		180,600	173,700
Discharge in main channel of contracted (bridge) section (ft3/s)	Q2		155,800	148,100	143,400		182,200	176,600
Width of main channel of approach section (ft)	W1		796	796	796		796	796
Width of main channel of contracted (bridge) section (ft)	W2		706	706	710		706	710
Average depth of main channel of approach section (ft)	y1		20.7	19.1	22.2		20.9	23.8
Average depth in contracted (bridge) section (ft)	y2		22.3	20.7	24.2		22.9	26.2
Contraction Scour (ft)	ycs		1.7	1.7	2.0		2.0	2.3

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